Quantitative Applications Of Raman Technique For Deep-sea Environment And Sediment Detection

The Raman technique as a qualitative technique has already been used with deep sea ROV platforms successfully performing in situ measurement on targets of scientific interest including gas and hydrothermal vent fluids, and complex gas hydrates. In this thesis, by self-referencing to the ubiquitous water peaks, quantitative informations have been derived for deep-sea environment and sediment detection.A ROV-deployable sampling probe utilizing laser Raman spectroscopy for study of sediment pore water geochemistry has been developed. This design incorporates a series of novel elements into a slender 30-cm-long probe that can be inserted into sediment using an ROV manipulator to obtain concentration profiles. Pore water is drawn forms the probe tip into a low volume sample chamber (0.1-mL) using a small hydraulic pump controlled by the ROV. The sampling process is repeated as we proceed incrementally deeper into the sediment. Control of the Raman system and spectra acquisition are performed onboard the ship via a laptop computer in the ROV control room.The flux of dissolved methane through continental margin sediments is of importance in marine geochemistry due to its role in massive hydrate formation with enigmatic climate consequences, and for the huge and complex microbial assemblage it supports. The thesis shows that accurate quantitative measurement of pore water profiles of dissolved CH4, SO4, and H2S can be made rapidly in situ using a Raman-based probe without incurring substantial degassing during core recovery. Results from Hydrate Ridge, Oregon clearly show coherent profiles of all these species in this high flux environment, and while in situ Raman and conventional analyses of SO4 in recovered cores agree well, very large differences in CH4 are found. Profiles obtained in situ showed minimal fluorescence while pore water samples from recovered cores quickly developed strong fluorescence making laboratory analyses using Raman spectroscopy challenging and raising questions over the reaction sequence responsible for this.The long-term fate of chemical weapon debris disposed of in the ocean some 50 years ago. Direct evidence exists showing chemical weapon agents actively being released on the sea floor with detrimental effects including harm to marine life. Thus there is strong interest in determining their decomposition products, and the affected zones around these sites. Here we study the geochemical properties of a mustard gas breakdown product, 1,4-thioxane (TO), using Raman spectroscopy. We show that TO forms a hydrate with a help-gas, such as methane or hydrogen sulphide. The temperature, pressure and reducing conditions required for hydrate formation commonly occur at known disposal sites. The TO solubility was measured in sea water. A low solubility in water coupled with its ability to form a hydrate within marine sediments can greatly decrease molecular mobility and increase its lifetime.